The big mistake the Dolphins made in this area was in thinking Suh would have the effect on opposing passing games necessary to supplement Tannehill's typical level of play and make the team a Super Bowl contender.
They're paying both players as though they'd give the team the passer rating differential necessary to accomplish that, whereas Suh is obviously having no such effect on opposing passing games. The team's pass defense is horrendous despite Suh's presence, and the team is going nowhere with a pass defense this poor.
Now they're stuck in a situation in which both players are (or will be) on the wrong side of 30 and wouldn't fetch as much in trade as they would have earlier in their careers. Also at issue is the fact that trading Suh would result in $22M in dead cap money, with only a $3.9M cap savings in 2018.
That said, however, with the team's being a ways off from contending, it would make sense to trade Suh for even something as meager as a 4th- or 5th-round pick. Essentially you'd be trading Suh for something meager, in exchange for the other team's willingness to take on his salary.
The alternative is that you wait another year, Suh is a year older, and teams are unwilling perhaps to part with anything for him, knowing the Dolphins can then cut him and save $15M against the cap.
In other words, this may be the last year anything at all can be gotten for Suh in trade. If his career longevity doesn't fit this team's view of its longer-term building process, it's time to trade him now, while something can still be garnered in return.
I strongly doubt the team can improve enough in just the 2017/2018 offseason to warrant viewing Suh as an integral piece of a Super Bowl push. It's time to realize he just doesn't fit anymore.
I think what you're saying is that BAD decisions lead to bad results and poor options...